20 Spatial Aggregate Functions

This chapter contains reference and usage information for the spatial aggregate functions, which are listed in Table 20-1.

Table 20-1 Spatial Aggregate Functions

Method	Description
SDO_AGGR_CENTROID	Returns a geometry object that is the centroid ("center of gravity") of the specified geometry objects.
SDO_AGGR_CONCAT_LINES	Returns a geometry that concatenates the specified line or multiline geometries.
SDO_AGGR_CONVEXHULL	Returns a geometry object that is the convex hull of the specified geometry objects.
SDO_AGGR_LRS_CONCAT	Returns an LRS geometry object that concatenates specified LRS geometry objects.
SDO_AGGR_MBR	Returns the minimum bounding rectangle of the specified geometries.
SDO_AGGR_SET_UNION	Takes a VARRAY of SDO_GEOMETRY objects as input, and returns the aggregate union of all geometry objects in the array.
SDO_AGGR_UNION	Returns a geometry object that is the topological union (OR operation) of the specified geometry objects.

See the usage information about spatial aggregate functions in Section 1.10.

Most of these aggregate functions accept a parameter of type SDOAGGRTYPE, which is described in Section 1.10.1.

Note:

Spatial aggregate functions are supported for two-dimensional geometries only, except for SDO_AGGR_MBR, which is supported for both two-dimensional and three-dimensional geometries.

SDO_AGGR_CENTROID

Format

SDO_AGGR_CENTROID(

AggregateGeometry SDOAGGRTYPE

) RETURN SDO_GEOMETRY;

Description

Returns a geometry object that is the centroid ("center of gravity") of the specified geometry objects.

Parameters

AggregateGeometry: An object of type SDOAGGRTYPE (see Section 1.10.1) that specifies the geometry column and dimensional array.

Usage Notes

The behavior of the function depends on whether the geometry objects are all polygons, all points, or a mixture of polygons and points:

If the geometry objects are all polygons, the centroid of all the objects is returned.
If the geometry objects are all points, the centroid of all the objects is returned.
If the geometry objects are a mixture of polygons and points (specifically, if they include at least one polygon and at least one point), any points are ignored, and the centroid of all the polygons is returned.

The result is weighted by the area of each polygon in the geometry objects. If the geometry objects are a mixture of polygons and points, the points are not used in the calculation of the centroid. If the geometry objects are all points, the points have equal weight.

See also the information about the SDO_GEOM.SDO_CENTROID function in Chapter 24.

Examples

The following example returns the centroid of the geometry objects in the COLA_MARKETS table. (The example uses the definitions and data from Section 2.1.)

SELECT SDO_AGGR_CENTROID(SDOAGGRTYPE(shape, 0.005))
  FROM cola_markets;

SDO_AGGR_CENTROID(SDOAGGRTYPE(SHAPE,0.005))(SDO_GTYPE, SDO_SRID, SDO_POINT
--------------------------------------------------------------------------------
SDO_GEOMETRY(2001, NULL, SDO_POINT_TYPE(5.21295938, 5.00744233, NULL), NULL, NUL
L)

SDO_AGGR_CONCAT_LINES

Format

SDO_AGGR_CONCAT_LINES(

geom SDO_GEOMETRY

) RETURN SDO_GEOMETRY;

Description

Returns a geometry that concatenates the specified line or multiline geometries.

Parameters

geom: Geometry objects.

Usage Notes

Each input geometry must be a two-dimensional line or multiline geometry (that is, the SDO_GTYPE value must be 2002 or 2006). This function is not supported for LRS geometries. To perform an aggregate concatenation of LRS geometric segments, use the SDO_AGGR_LRS_CONCAT spatial aggregate function.

The input geometries must be line strings whose vertices are connected by straight line segments. Circular arcs and compound line strings are not supported.

If any input geometry is a multiline geometry, the elements of the geometry must be disjoint. If they are not disjoint, this function may return incorrect results.

The topological relationship between the geometries in each pair of geometries to be concatenated must be DISJOINT or TOUCH; and if the relationship is TOUCH, the geometries must intersect only at two end points.

You can use the SDO_UTIL.CONCAT_LINES function (described in Chapter 32) to concatenate two line or multiline geometries.

An exception is raised if any input geometries are not line or multiline geometries, or if not all input geometries are based on the same coordinate system.

Examples

The following example inserts two line geometries in the COLA_MARKETS table, and then returns the aggregate concatenation of these geometries. (The example uses the data definitions from Section 2.1.)

-- First, insert two line geometries.
INSERT INTO cola_markets VALUES(1001, 'line_1', SDO_GEOMETRY(2002, NULL, NULL, 
  SDO_ELEM_INFO_ARRAY(1,2,1), SDO_ORDINATE_ARRAY(1,1, 5,1)));
INSERT INTO cola_markets VALUES(1002, 'line_2', SDO_GEOMETRY(2002, NULL, NULL, 
  SDO_ELEM_INFO_ARRAY(1,2,1), SDO_ORDINATE_ARRAY(5,1, 8,1)));
-- Perform aggregate concatenation of all line geometries in layer.
SELECT SDO_AGGR_CONCAT_LINES(c.shape) FROM cola_markets c
   WHERE c.mkt_id > 1000;

SDO_AGGR_CONCAT_LINES(C.SHAPE)(SDO_GTYPE, SDO_SRID, SDO_POINT(X, Y, Z), SDO_ELEM
--------------------------------------------------------------------------------
SDO_GEOMETRY(2002, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 2, 1), SDO_ORDINATE_ARRAY(
1, 1, 5, 1, 8, 1))

SDO_AGGR_CONVEXHULL

Format

SDO_AGGR_CONVEXHULL(

AggregateGeometry SDOAGGRTYPE

) RETURN SDO_GEOMETRY;

Description

Returns a geometry object that is the convex hull of the specified geometry objects.

Parameters

AggregateGeometry: An object of type SDOAGGRTYPE (see Section 1.10.1) that specifies the geometry column and dimensional array.

Usage Notes

See also the information about the SDO_GEOM.SDO_CONVEXHULL function in Chapter 24.

Examples

The following example returns the convex hull of the geometry objects in the COLA_MARKETS table. (The example uses the definitions and data from Section 2.1.)

SELECT SDO_AGGR_CONVEXHULL(SDOAGGRTYPE(shape, 0.005))
  FROM cola_markets;

SDO_AGGR_CONVEXHULL(SDOAGGRTYPE(SHAPE,0.005))(SDO_GTYPE, SDO_SRID, SDO_POI
--------------------------------------------------------------------------------
SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 1003, 1), SDO_ORDINATE_ARR
AY(8, 1, 10, 7, 10, 11, 8, 11, 6, 11, 1, 7, 1, 1, 8, 1))

SDO_AGGR_LRS_CONCAT

Format

SDO_AGGR_LRS_CONCAT(

AggregateGeometry SDOAGGRTYPE

) RETURN SDO_GEOMETRY;

Description

Returns an LRS geometry that concatenates specified LRS geometries.

Parameters

AggregateGeometry: An object of type SDOAGGRTYPE (see Section 1.10.1) that specifies the geometry column and dimensional array.

Usage Notes

This function performs an aggregate concatenation of any number of LRS geometries. If you want to control the order in which the geometries are concatenated, you must use a subquery with the NO_MERGE optimizer hint and the ORDER BY clause. (See the examples.)

The direction of the resulting segment is the same as the direction of the first geometry in the concatenation.

A 3D format of this function (SDO_AGGR_LRS_CONCAT_3D) is available. For information about 3D formats of LRS functions, see Section 7.4.)

For information about the Spatial linear referencing system, see Chapter 7.

Examples

The following example adds an LRS geometry to the LRS_ROUTES table, and then performs two queries that concatenate the LRS geometries in the table. The first query does not control the order of concatenation, and the second query controls the order of concatenation. Notice the difference in direction of the two segments: the segment resulting from the second query has decreasing measure values because the first segment in the concatenation (Route0) has decreasing measure values. (This example uses the definitions from the example in Section 7.7.)

-- Add a segment with route_id less than 1 (here, zero).
INSERT INTO lrs_routes VALUES(
  0,
  'Route0',
  SDO_GEOMETRY(
    3302,  -- Line string; 3 dimensions (X,Y,M); 3rd is measure dimension.
    NULL,
    NULL,
    SDO_ELEM_INFO_ARRAY(1,2,1), -- One line string, straight segments
    SDO_ORDINATE_ARRAY(
      5,14,5,   -- Starting point - 5 is measure from start.
      10,14,0)  -- Ending point - 0 measure (decreasing measure)
  )
);

1 row created.

-- Concatenate all routes (no ordering specified).
SELECT SDO_AGGR_LRS_CONCAT(SDOAGGRTYPE(route_geometry, 0.005))
    FROM lrs_routes;

SDO_AGGR_LRS_CONCAT(SDOAGGRTYPE(ROUTE_GEOMETRY,0.005))(SDO_GTYPE, SDO_SRID
--------------------------------------------------------------------------------
SDO_GEOMETRY(3302, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 2, 1), SDO_ORDINATE_ARRAY(
2, 2, 0, 2, 4, 2, 8, 4, 8, 12, 4, 12, 12, 10, 18, 8, 10, 22, 5, 14, 27, 10, 14, 
32))

-- Aggregate concatenation using subquery for ordering.
SELECT 
SDO_AGGR_LRS_CONCAT(SDOAGGRTYPE(route_geometry, 0.005)) 
FROM ( 
             SELECT /*+ NO_MERGE */ route_geometry 
             FROM lrs_routes 
             ORDER BY route_id); 

SDO_AGGR_LRS_CONCAT(SDOAGGRTYPE(ROUTE_GEOMETRY,0.005))(SDO_GTYPE, SDO_SRID
--------------------------------------------------------------------------------
SDO_GEOMETRY(3302, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 2, 1), SDO_ORDINATE_ARRAY(
2, 2, 32, 2, 4, 30, 8, 4, 24, 12, 4, 20, 12, 10, 14, 8, 10, 10, 5, 14, 5, 10, 14
, 0))

SDO_AGGR_MBR

Format

SDO_AGGR_MBR(

geom SDO_GEOMETRY

) RETURN SDO_GEOMETRY;

Description

Returns the minimum bounding rectangle (MBR) of the specified geometries, that is, a single rectangle that minimally encloses the geometries.

Parameters

geom: Geometry objects.

Usage Notes

This function does not return an MBR geometry if a proper MBR cannot be constructed. Specifically:

If the input geometries are all null, the function returns a null geometry.
If all data in the input geometries is on a single point, the function returns the point.
If all data in the input geometries consists of points on a straight line, the function returns a two-point line.

The SDO_TUNE.EXTENT_OF function, documented in Chapter 31, also returns the MBR of geometries. The SDO_TUNE.EXTENT_OF function has better performance than the SDO_AGGR_MBR function if the data is non-geodetic and if a spatial index is defined on the geometry column; however, the SDO_TUNE.EXTENT_OF function is limited to two-dimensional geometries, whereas the SDO_AGGR_MBR function is not. In addition, the SDO_TUNE.EXTENT_OF function computes the extent for all geometries in a table; by contrast, the SDO_AGGR_MBR function can operate on subsets of rows.

Examples

The following example returns the minimum bounding rectangle of the geometry objects in the COLA_MARKETS table. (The example uses the definitions and data from Section 2.1.)

SELECT SDO_AGGR_MBR(shape) FROM cola_markets;

SDO_AGGR_MBR(C.SHAPE)(SDO_GTYPE, SDO_SRID, SDO_POINT(X, Y, Z), SDO_ELEM_INFO, SD
--------------------------------------------------------------------------------
SDO_GEOMETRY(2003, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 1003, 3), SDO_ORDINATE_ARR
AY(1, 1, 10, 11))

SDO_AGGR_SET_UNION

Format

SDO_AGGR_SET_UNION(

geometry SDO_GEOMETRY_ARRAY

tol NUMBER

) RETURN SDO_GEOMETRY;

Description

Takes a VARRAY of SDO_GEOMETRY objects as input, and returns the aggregate union of all geometry objects in the array.

Parameters

geometry: An array of geometry objects of object type SDO_GEOMETRY_ARRAY, which is defined as VARRAY OF SDO_GEOMETRY.
tol: Tolerance value (see Section 1.5.5).

Usage Notes

SDO_AGGR_SET_UNION provides faster performance than SDO_AGG_UNION but less flexibility, and SDO_AGGR_SET_UNION should be considered when performance is especially important and when it satisfies your functional needs.

SDO_AGGR_UNION is a SQL aggregate function, and therefore it very flexible and can be used with complex SQL GROUP BY clauses. However, SDO_AGGR_UNION is significantly slower than SDO_AGGR_SET_UNION due to the overhead of the SQL aggregation framework. SDO_AGGR_SET_UNION is useful when the geometries to be grouped can easily be gathered into a collection (that is, a VARRAY of SDO_GEOMETRY objects).

Examples

The following example creates a user-defined function to return an array of all cola market geometries except cola_d, and then uses the SDO_AGGR_SET_UNION function to return the aggregate union of the geometry objects in that array. (The example uses the definitions and data from Section 2.1, and the objects in the array will be cola_a, cola_b, and cola_c.)

CREATE OR REPLACE FUNCTION Set_Geometry RETURN SDO_GEOMETRY_ARRAY deterministic AS
  type        cursor_type is REF CURSOR;
  query_crs   cursor_type;
  g           sdo_geometry;
  GeometryArr sdo_geometry_array;
BEGIN
  GeometryArr := SDO_GEOMETRY_ARRAY();
  OPEN query_crs FOR 'select shape FROM cola_markets c WHERE c.name <> ''cola_d'' ';
   LOOP
    FETCH query_crs into g;
     EXIT when query_crs%NOTFOUND ;
     GeometryArr.extend;
     GeometryArr(GeometryArr.count) := g;
   END LOOP;
   RETURN GeometryArr;
END;
/

Function created.

SELECT SDO_AGGR_SET_UNION(Set_Geometry, 0.005) FROM DUAL;

SDO_AGGR_SET_UNION(SET_GEOMETRY,0.005)(SDO_GTYPE, SDO_SRID, SDO_POINT(X, Y, Z), 
--------------------------------------------------------------------------------
SDO_GEOMETRY(2004, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 2, 1, 5, 1003, 1, 19, 2003
, 1), SDO_ORDINATE_ARRAY(5, 3, 5, 5, 5, 1, 8, 1, 8, 6, 5, 7, 1, 7, 1, 1, 5, 1, 5
, 3, 3, 3, 4, 5, 5, 5, 6, 5, 6, 3, 5, 3))

SDO_AGGR_UNION

Format

SDO_AGGR_UNION(

AggregateGeometry SDOAGGRTYPE

) RETURN SDO_GEOMETRY;

Description

Returns a geometry object that is the topological union (OR operation) of the specified geometry objects.

Parameters

AggregateGeometry: An object of type SDOAGGRTYPE (see Section 1.10.1) that specifies the geometry column and dimensional array.

Usage Notes

Do not use SDO_AGGR_UNION to merge line string or multiline string geometries; instead, use the SDO_AGGR_CONCAT_LINES spatial aggregate function.

See also the information about the SDO_GEOM.SDO_UNION function in Chapter 24.

Examples

The following example returns the union of all geometries except cola_d (in this case, cola_a, cola_b, and cola_c). (The example uses the definitions and data from Section 2.1.)

SELECT SDO_AGGR_UNION(
  SDOAGGRTYPE(c.shape, 0.005))
  FROM cola_markets c
  WHERE c.name <> 'cola_d';

SDO_AGGR_UNION(SDOAGGRTYPE(C.SHAPE,0.005))(SDO_GTYPE, SDO_SRID, SDO_POINT(
--------------------------------------------------------------------------------
SDO_GEOMETRY(2007, NULL, NULL, SDO_ELEM_INFO_ARRAY(1, 1003, 2, 11, 1003, 1), SDO
_ORDINATE_ARRAY(8, 11, 6, 9, 8, 7, 10, 9, 8, 11, 1, 7, 1, 1, 5, 1, 8, 1, 8, 6, 5
, 7, 1, 7))

See also the more complex SDO_AGGR_UNION example in Section C.4.